It is desirable to produce blow-molded articles which are free of cutout plugs using conventional blow-molding needles. Cutout plugs are formed by a hollow-tipped blow-molding needle piercing a parison.
Conventional blow-molding needles are generally an extended tube terminating in a bevelled tip. The perimeter of the tubular portion acts as a cutting surface. These needles are herein referred to as hollow-tipped. Hollow-tip blow-molding needles penetrate a parison wall by cutting a circular opening in the parison. A circular cutout plug is produced. The cutout interferes with subsequent processing of the blow-molded article. The cutout may fall within the molded article requiring subsequent removal, or the cutout plug may fold back within the parison and adhere to the back wall of the parison. The cutout plug may interfere with subsequent processing of the molded article, or may become detached after the blow molding. Subsequent detachment may interfere with the operation of the molded article by clogging passages or produce rattles.
U.S. Pat. No. 4,859,397 issued to Peters, Aug. 22, 1989 and incorporated herein by reference teaches the blow molding a parison using a hollow-tipped blow-molding needle. A hollow-tipped blow-molding needle comprising a hollow tube having a beveled portion tapering into a sharp point is used to pierce a parison. The blow-molding needle is actuated linearly between a retracted and extended position in a die piece. It is believed that as the hollow-tipped needle pierces the parison, a circular cutout is created. The cutout either falls within the parison and is subsequently removed or folds back upon the interior parison wall. A shoulder sealing having one or more projections, aids in sealing between the parison and needle.
U.S. Pat. No. 3,450,805, issued to Chesser, June 17, 1969 also teaches a process of blow-molding a molded article. An extruder extrudes a length of thermoformable parison. A mandrel partially inflates the parison. Mold die pieces close about the parison pinching the parison closed. A bevel pointed blow-molding needle having one or more outlets near the pointed end pierces the parison. The outlets are arranged around the periphery of the point bevel. This arrangement causes fluid flowing through the needle to diffuse at the outlets and prevent blistering of the parison. The bevel-pointed blow-molding needle eliminates the cutout but is difficult to use when blow-molding relatively thick parisons on the order of 4-7 mm. The bevel-point is believed to form an extended ridge around the interior perimeter of the parison opening. This extended ridge may interfere with subsequent processing of the molded article.
U.S. Pat. No. 3,821,344, issued to Peters, June 28, 1974 teaches a bevel point or knife edge for a mandrel that pierces the parison after the molded article is fully inflated by a blow pin. The mandrel sizes an opening in the parison for a neck portion. The knife edge is not used for a blow-molding needle.
U.S. Pat. No. 3,167,817 issued to Zalkind Feb. 2, 1965, teaches a four-bladed Phillips screwdriver bit for boring a blow-molded article The bit is ground to a sharp point. Flutes on the bit have sharp edges to effect a grinding or cutting away of the plastic material. The bit is not used as a needle and does not pierce a parison. Rather, this bit is used to bore through a molded article.
It is desirable to provide a method of blow-molding a parison which eliminates a cutout from a blow-molding needle. It is also desirable to provide an arrow-tipped blow-molding needle which pierces a parison wall to form flap sections. The flap sections fold inward against the parison wall. It is still a further object of the present invention to provide a blow-molding needle which reduces the amount of debris collected in a blow-molding needle.